FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1925
1925 - 0826.PDF
DECEMBER 17, 1925 AIR SURVEYING 15,000 SQUARE MILES OF FOREST IN BURMA IN our report on Major C. K. Cochran-Patrick's Paper, " Air Surveys in Burma," read before the Royal Aeronautical Society recently, which we published in our issue of November 5, we made only passing reference to that section of the paper dealing with the forest stocking of 15,000 square miles of South Burma. As we stated at the time, we had not then the space for a full quotation of Major Cochran-Patrick's very interesting story of this section of their activities in Burma but promised to give our readers the full account on another occasion. This week, therefore, we publish this section of Major Cochran-Patrick's paper, and think our readers will agree that it makes interesting reading. " The Tenasserim Reconnaissance area surveyed which stretches from Heinze Bay to Victoria Point, consists of a long narrow strip bounded by the coast to the west and the high hills of the. Siamese border to the east. There are only three towns of any importance in the area, Tavoy, Mergui and Victoria Point. These are connected by a weekly steamer service with Rangoon and a fortnighly service from Mergui to Victoria Point which calls at Karathuri. " Besides this main service and local motor-boat services for short distances up the Tavoy River and along the coast to a point about 60 miles south of Mergui there is absolutely no regular communication and only indifferent tracks between native villages. As it was important to economise in flying time it was obvious that we would have to work from a series of bases. We had therefore to arrange to be self-supporting and self-transporting. For this purpose, Mr. Kemp brought out from England a converted naval pinnace boat which had been fitted with a paraffin engine. She was capable of doing eight knots, of standing a reasonable amount of bad weather, and of sleeping, besides native crew, two Europeans comfort- ably or four at a pinch. " We had contracted to undertake a certain number of flying hours and to photograph an area of not more than 600 sq. miles of forest reserve near Heinze Bay- The flying hours were to be occupied in taking a forest officer over such area as they required for the purpose of making a forest stock map by sketching on to existing maps. The forest officer in charge had the option of converting square miles of photography into hours flying time at a pre-arranged rate if, after trying both, he considered that the sketching method was more satisfactory for the work in hand than the photo- graphic. "The forest officers with whom we had to work were Messrs. C. W. Scott and C. R. Robbins, who were responsible for the stock mapping of the Irrawaddy Delta. These gentlemen spent a month or two examining small portions of the area on foot in order to get some preliminary,idea of the type of timber that they might expect to find, and it was arranged that we should meet them at our first base in Heinze Ba3'. " The party therefore consisted of the two forest officers and myself, who took our tents and lived ashore. Mr. Bishop, our foreman fitter and also captain and navigator of the launch, and Mr. Andrews, the photographer, lived on the launch. One aero engine native fitter, who acted as engineer for the launch, and various native crew and boys were housed where most convenient We also took two native photographic assistants to the first base, where the bulk of the photography was to be done. " On January 10 Kemp left Rangoon with the launch loaded with petrol and gear for Heinze Bay and three days later I flew the machine down without incident. The site of our first base was alongside the only piece of hard beach in Heinze Bay, which is in general surrounded by mangroves and mud. The water only reached this bit of beach over the mud after three-quarter tide. As it was important to be able to work at all states of tide the seaplane had to be moored out. The forest officers had both arrived by dug-out before the aeroplane and had got their camp pitched, and Kemp left for Rangoon via the Tavoy River the day after I got down Cloud conditions were not very favourable, but we succeeded in photographing two areas of 100 sq. miles each and in doing the first sketching flights without much delay. " It was then decided to transfer the remainder of the photography to reconnaissance time as it was found that a sufficiently high order of accuracy could be attained by sketching for the particular work in hand and "the very considerable additional cost of the photography, when taken on a square mile basis, was not justified. " This principle having been decided, a definite programme of work was drawn up in order to avoid all possible waste of flying time. The problem divides itself into three parts :— (a) Safety. (b) Visibility of detail, and (c) Map reading and sketching. " From the point of view of safety, in all but the most ideal country one should of course.fly as high as possible in order to have a maximum choice of landing'grounds. For visibility of detail, on the other hand, the lower the observer flies the more he sees, though there is a definite limit to this as at a very low altitude the tendency is to lose sight of the wood for the trees. " The third factor of map reading and sketching comes between the other two and is finally the governing factor. The larger the scale map used the more difficult it is to read from the air. The higher nnd slower one flies the easier it is to read any map. " Therefore for a given scale map and a given cruising speed there is a definite height below which an observer has not time to read his map and the minimum height is consider- ably increased when he has also to find time to sketch in detail on the map. " Actually we found 8,000—10,000 ft. to be the most suitable height for the work in hand. It was the cruising ceiling of the particular machine we were using, and therefore complied to the maximum possible with the safety clause. Robbins found that he could see all the detail required with ease, in fact when we got the second machine later on, which went to 13,000 ft., he found that he could still see all necessary detail from that height. On the other hand, with the wonder- ful general view of forest seen from 10,000 ft, there was no temptation to endeavour to put in too small items of detail which would have been irrelevant to the particular needs of this reconnaissance. As regards map reading and sketching, the ideal aimed at was to do all work in a series of straight lines without having to resort to circling. Working at 80 ni.p.h. on one inch maps at 10,000 ft. it was found that in virgin forest where types stretched over big areas without much variation, the observer could work on both sides of the machine. In areas where cultivation had occurred or types were very mixed, the observer worked on the one side only. It was very occasionally that any circling had to be done to give time for filling in even the most complicated detail. " The programme for each flight was carefully worked out beforehand and usually consisted of a straight flight out and a series of parallel short strips at right angles to this working back to the base and forming an area like the section of a fan. These sections, when joined together fanlike with our base as the handle, formed the most economical method of covering the area. " The photography and reconnaissance for the northern section was completed in this manner in eleven days during which we made nine flights. Kemp had intended to recon- noitre a site for our next base at the Tavoy mouth on his way to Rangoon, but as we received no news from him we flew down and inspected the spot from the air. The ideal position lay behind some islands, but the channels looked shallow and we were doubtful as to whether our launch could get in so we decided to try outside. The machine was brought ashore and the floats repainted, oil changed, etc. Scott then went off by dug-out to work his way down to • Tavoy mouth with the tents and heavy gear. Robbins and I filled the seaplane with kit and a heavy anchor in addition to the usual one and, leaving the launch to follow, flew south. We landed and found a strong tide running out. The light machine anchor did not even slow up our drift. The heavy anchor, a 76-lb. one, was put down as quickly as possible but we still drifted. A native boat chose this awkward moment to get upstream of us and then lose control. We just managed to keep him clear of the 'planes, and while Robbins broke our paddle on the steersman's back I borrowed their anchor which happened to be a good big one. The third anchor stopped our drift and we had a chance to get everything shipshape on the turn of the tide. " Nevertheless, we decided to cook and sleep on the machine in case of accidents. Luckily our triple anchors held and the night passed without any more drifting. Next morning Robbins went off and found that the channels behind 826
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
